1. Field of the Invention
This invention relates to seat cushions, more particularly to a seat cushion that improves seating posture by applying torque to the ischial tuberosities of the pelvic bones and the gluteal muscles of a user.
2. Brief Description of the Prior Art
It is estimated that almost half of the population of the industrialized world is suffering from back disorders of various forms. Vast sums are spent on medical treatment, disability pay, rehabilitation and the like related to these problems. Treatment often does not begin, however, until a cure is not possible. Studies indicate that sitting causes greater strain on the lower spine than standing or bending and that higher levels of degeneration of the bones, discs, musoles, and ligaments of the lower back have been found in sedentary workers than in those handling heavy materials. For this reason, a great deal of effort has been directed toward developing ergometric seating apparatus that prevents back pain and injury through the promotion of good seating posture.
It is known that sitting reduces the normal lumber curve (extension, lordosis). Prolonged exposure to this posture can produce low back pains and even disc degeneration. A. C. Mandal, in the March, 1981, issue of Applied Ergonomics, suggests that a forward angle tilt of 20 degrees in the seat pan will maintain lordosis.
In the past, when most workers spent most of the working day standing or lifting, flat chairs were appropriate to help relieve symptoms of hyper extension of the lumber curve (swayback). With modern workers spending most of their time sitting, hypolordic posture is of more concern. The common flat seated chair in the modern workplace is implicated in the creation of back pain by stretching the posterior longitudinal ligaments, and may even distort the intervertebral discs. Modern day workers, then, need seats which will, as Mandal suggests, slant forward to help maintain the lordic curve.
Modern orthopedic chairs, costing $400 or more, are available which allow a certain degree of forward tilt. The primary disadvantage of a seat having sufficient forward slant to solve the postural problem is that the sitter tends to slide down and off. This causes the sitter to tense up, which negates any posture benefits, because of the discomfort and attention required to maintain one's position. An attempt to correct this resulted in the kneeling or Balans chair, which utilizes a pad upon which the knees rest. The pressure from the pad on the knees prevents the sitter from sliding forward due to the forward tilt of the seat. One disadvantage of this chair is that prolonged sitting in it becomes uncomfortable for the knees. Also, it is cumbersome to get in and out of.
Perhaps the most common solution at this time is the lumbar support cushion, which applies pressure to the apex of the lumbar curve to help maintain it. Its primary disadvantage is that the sitter needs to be sitting back at an angle great enough to apply pressure on the spine for such a cushion to be effective. This is an uncommon situation in the workplace. Also, any pressure on the spine may inhibit the cranio-sacral rhythm, and therefore, the circulation of cerebrospinal fluid.
Prior developments in this field may be generally illustrated by reference to the following patents:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,218,792 H. Kogan Aug. 26, 1980 1,716,871 E. Weldon June 11, 1929 3,503,649 M. Johnson Mar. 31, 1970 3,376,070 M. Johnson Apr. 02, 1968 2,855,986 B. Engelen, Sr. Oct. 14, 1958 3,394,414 L. Unger July 30, 1968 3,846,857 C. Weinstock Nov. 12, 1974 2,412,112 G. Wood et al. Dec. 03, 1946 2,156,629 M. Hutchinson May 02, 1939 ______________________________________